jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML. Used by over 60% of the 10,000 most visited websites, jQuery is the most popular JavaScript library in use today. jQuery is free, open source software, licensed under the MIT License.

jQuery''s syntax is designed to make it easier to navigate a document, select DOM elements, create animations, handle events, and develop Ajax applications. jQuery also provides capabilities for developers to create plug-ins on top of the JavaScript library. This enables developers to create abstractions for low-level interaction and animation, advanced effects and high-level, theme-able widgets. The modular approach to the jQuery library allows the creation of powerful dynamic web pages and web applications.

The set of jQuery core features—DOM element selections, traversal and manipulation—enabled by its selector engine (named "Sizzle" from v1.3), created a new "programming style", fusing algorithms and DOM-data-structures. This style influenced the architecture of other JavaScript frameworks like YUI v3 and Dojo, later stimulating the creation of the standard Selectors API.

Microsoft and Nokia bundle jQuery on their platforms. Microsoft includes it with Visual Studio for use within Microsoft''s ASP.NET AJAX framework and ASP.NET MVC Framework while Nokia has integrated it into the Web Run-Time widget development platform. jQuery has also been used in MediaWiki since version 1.16.

Contents

1 Overview

2 Features

2.1 Browser support

3 Usage

3.1 Including the library

3.2 Usage styles

3.3 No-Conflict Mode

3.4 Typical start-point

3.5 Chaining

3.6 Creating new DOM elements

3.7 Utility Functions

3.8 AJAX

4 jQuery plug-ins

5 History

5.1 Release history

6 Testing framework

7 See also

8 References

9 Further reading

10 External links

Overview

jQuery, at its core, is a DOM manipulation library. The DOM is a tree structure representation of all the elements of a web-page and jQuery makes finding, selecting, and manipulating these DOM elements very simple and convenient. For example, jQuery can be used for finding an element in the document with a certain property (e.g. all elements with an h1 tag), changing one or more of its attributes (e.g. color, visibility), or making it respond to an event (e.g. a mouse click).

However, beyond basic DOM selecting and manipulation, jQuery provides a new paradigm of writing event handling in Javascript. The event assignment and the event callback function are done in a single step in a single location in the code. jQuery also aims to incorporate other highly used Javascript functionalities (e.g. fade ins and fade outs when hiding elements, animations by manipulating CSS properties).

The advantages of using jQuery are:

Separates Javascript and HTML: Instead of using HTML attributes to call Javascript functions for event handling, jQuery allows all event-handling functions to be done purely in Javascript. Thus, the HTML tags and Javascript can be completely separated.

Eliminates cross-browser incompatibilities: The Javascript engines of different browsers differ slightly, so Javascript code that works for one browser may not work on the other. jQuery handles all these cross-browser inconsistencies and provides a consistent interface that works across different browsers.

Extensible: jQuery makes extending the framework very simple. New events, elements and methods can be easily added and then reused as a plugin.

Features

jQuery includes the following features:

DOM element selections using the multi-browser open source selector engine Sizzle, a spin-off of the jQuery project

DOM traversal and modification (including support for CSS 1–3)

DOM manipulation based on CSS selectors that uses node elements name and node elements attributes (id and class) as criteria to build selectors

Compatibility methods that are natively available in modern browsers but need fall backs for older ones - For example the inArray() and each() functions.

Multi-browser (not to be confused with cross-browser) support.

Browser support

Both version 1.x and 2.x of jQuery support "current-1 versions" (meaning the current stable version of the browser and the version that preceded it) of Firefox, Google Chrome, Safari, and Opera. The version 1.x also supports Internet Explorer 6 or higher. However, jQuery version 2.x dropped Internet Explorer 6–8 support (which represents less than 28% of all browsers in use) and can run only with IE 9 or higher.

Usage Including the library

The jQuery library is a single JavaScript file, containing all of its common DOM, event, effects, and Ajax functions. It can be included within a web page by linking to a local copy, or to one of the many copies available from public servers. jQuery has a CDN hosted by MaxCDN (moved from MediaTemple and, before that, Amazon). Google and Microsoft host it as well.

<script src="jquery.js"></script>

It is also possible to include jQuery directly from content delivery networks.

Via the $ function, which is a factory method for the jQuery object. These functions, often called commands, are chainable as they all return jQuery objects.

Via $.-prefixed functions. These are utility functions, which do not act upon the jQuery object directly.

Typically in jQuery, access to and manipulation of multiple DOM nodes begins with the $ function being called with a CSS selector string. This returns a jQuery object referencing all the matching elements in the HTML page and all its methods. For example, $("div.test") returns a jQuery object with all the div elements of class test with all its methods. This node set can be manipulated by calling instance methods on the returned jQuery object, or on the nodes themselves.

No-Conflict Mode

jQuery also includes .noConflict() mode, which relinquishes control of $. This can be helpful if jQuery is being used with other libraries that happen to use $ as well. In no-conflict mode, developers can use jQuery as a replacement for $, without losing functionality.

Typical start-point

The typical jQuery usage is to put initialization code and event handling functions in .ready(). This is triggered when the browser has constructed the DOM and sends a load event.

Callback functions for event handling are also included inside .ready() as anonymous functions but called when the event for the callback is triggered. For example, the following jQuery code adds an event handler for a mouse click on an img image element.

Each jQuery command returns a jQuery object back and thus, we can further call functions on the returned objects resulting in a chain of commands called chaining. For example,

$("div.test").add("p.quote").addClass("blue").slideDown("slow");

This line finds the union of all div tags with class attribute test and all p tags with CSS class attribute quote, adds the class attribute blue to each matched element, and then increases their height with an animation. The $ and add functions affect the matched set, while the addClass and slideDown affect the referenced nodes.

Creating new DOM elements

Besides accessing DOM nodes through jQuery object hierarchy, it is also possible to create new DOM elements if a string passed as the argument to $() looks like HTML. For example, this line finds an HTML select element with ID carmakes, and adds an option element with value "VAG" and text "Volkswagen":

This example posts the data name=John and location=Boston to example.php on the server. When this request finishes successfully, the success function is called to alert the user. If the request fails, it will alert the user to the failure, the status of the request, and the specific error.

jQuery plug-ins

jQuery''s architecture allows developers to create plug-in code to extend its functionality. Currently there are thousands of jQuery plug-ins available on the web that cover a wide range of functionality such as Ajax helpers, web services, datagrids, dynamic lists, XML and XSLT tools, drag and drop, events, cookie handling, and modal windows.

An important source of jQuery plug-ins is the plugins subdomain of the jQuery Project website. However, in an effort to rid the site of spam, the plugins in this subdomain were accidentally deleted in December 2011. The new site will include a GitHub-hosted repository, which will require developers to resubmit their plugins and to conform to new submission requirements. There are alternative plug-in search engines like jquer.in that take more specialized approaches, such as listing only plug-ins that meet certain criteria (e.g. those that have a public code repository). jQuery provides a "Learning Center" which can help users understand JavaScript and get started developing jQuery plugins.

History

jQuery was originally released in January 2006 at BarCamp NYC by John Resig and was influenced by Dean Edwards'' earlier cssQuery library. It is currently maintained by a team of developers led by Dave Methvin.

Incorporated bug fixes and differences reported from both the 1.9 and 2.0 beta cycles

1.11

January 24, 2014 (2014-01-24)

1.11.1 (May 1, 2014 (2014-05-01))

93.5

2.0

April 18, 2013 (2013-04-18)

2.0.3 (July 3, 2013 (2013-07-03))

81.1

Dropped IE 6–8 support for performance improvements and reduction in filesize

2.1

January 24, 2014 (2014-01-24)

2.1.1 (May 1, 2014 (2014-05-01))

82.2

Testing framework

QUnit is a test automation framework used to test the jQuery project. The jQuery team developed it as an in-house unit testing library. The jQuery team uses it to test its code and plugins but it can test any generic JavaScript code, including server-side JavaScript code.

As of 2011, the jQuery Testing Team uses QUnit with TestSwarm to test each jQuery codebase release.